Means for and method of determining true north, latitude, and approximate sideral time, or any of them



Oct. 21 1924. 1,512,601

R. S. HQAR MEANS FOR AND METHOD @F.DETERMINTNG TRUE NORTH, LATITUDE, AND

APPROXIMATE SIDERAD TIME, 0R ANY oF THEM Filed May 21, 1919 Patented Oct. 21, 1924.

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l 1,512,6ti PATENT oFFi-CE.

ROGER SHERMAN HOAR, F CONCORD, MASSACHUSETTS, ASSIGNOR TO JOHN W. WEEKS, SECRETARY OF WAR ,0F THE UNITED STATES OF AMERICA, TRUSTEE.

MEANS FOR AND METHOD OF DETERMINING TRUE NORTH.,

LATITUDE, AND

APPROXIMATE SIDEBAL TIME, OR ANY OI@l THEM.

Application filed May 21, 1919. Serial No. 298,605.

(FILED UNDER THE ACT 0F MARCH 3, 1883, 22 STAT, L., 625.)

T 0 all 'LU/1.0m t may concern.'

Be it known that I, ROGER SHERMAN IIoAR, a citizen of the United States, and a resident of Concord, in the county of Middlesex and State of Massachusetts, have invented an Improvement in Means for and 'Methods of Determining True North, Latitude, and Approximate Sideral Time, or Any of rIhem, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

llt

The invention described herein may be used by the Government or any of its oliicers or employees in prosecution of work for the Government, or by any other person in the United' States without payment to me of any royalty thereon in accordance with the act of March 3, 1883.

This invention relates to means for and method of determiningtrue north, and more particularly it relates to a so-called Polaris attachment which may be used with an ordinary surveyors transit or like sighting in'- strument to determine the true north in the field, at any hour of the night, without reference to books or tables, with the. necessity for only one setting of the transit or other instrument, and without the necessity of knowing either the latitude or the time, even approximately.

In order that the principle of my iiivention may be readily understood, I shall describe one embodiment thereof and the best mode known to me for practising the method.

In the accompanying drawings:

rF ig. l is a perspective view of a transit having applied thereto one embodiment of my invention herein constituting an attachment or accessory therefor;

Fig. 2 is a plan view of the said attachment and Whereon I have indicated the plane of sight and also a line parallel to the so-called straight-edge;

Fig. 3 is a vertical section taken through thetube of the attachment and -represent- 'ing the prisms supported therein but not showing the so-called straight-edge;

Fig. 4 is a detail.l in side elevation of the interior of the tube and showing adjusting means for said prisms;

upon the Fig. 7 is a vertical section through a modified form of the attachment; and

Fig. 8 is a perspective of one of the prism rings, the other ring being a duplicate thereof.

'Ihe general principle of my invention is a mechanical lmeans for north-determination by the so-called hour angle method, the hour angle or sideral time being set by lining up an element of the invention onitwo stars.

In its simplest embodiment, to which, however, it is not restricted, my invention is a simple accessory for an ordinary surveyors transit or like instrument. Obviously it has a wide application of use. One extensive field of use is for orientation for heavy artillery, and by means of the invention the result obtained will be within the allowable error of precision for artillery work. North-determination by means of -my invention in its simplest embodiment is purely a field method, nol computations or even interpolations being involved. 'Ihe saine setting which gives the azimuth of the reference-line also gives the latitude and may be made to give the approximate sideral time siinplyl by graduating the cylinder of the attachment.

Before describing the illustrated form of the apparatus or means of my invention by detailed reference to the drawing, I will brieiy describe the same with general reference to its mode of use. In its disclosed form the attachment comprises a tube which may be generally similar, if desired, to the so-called sunshade that fits over the large end `of the telescope of the transit and just tight enough to allow free play. Tangent to a ring around this tube is what I term a straight-edge. Within the tube II provide preferably a pair of prisms which dedect the line of sight from the line of collimation by an an le equal to the mean polar distance of PoIaris as hereinafter disclosed. The straight-edge and the prisms are so Set with relation to each other that when the straight-edge is lined up with Polaris and. (5 Ursae Minoris (Polaris being at What'I term the P end'of the straight-edge), and

when the intersection of the cross wires of the transit is at the same time brought onto Polaris, the telescope Will then be pointed at the center of the circle described by Polaris, i. e: the Celestial North Pole.

Preferably the prisms are not achromatic. The result is that Polaris, instead of appearing as a point oit light, appears as a thin spectrum having a length between 1 and 2 of are. is the time of year changes, or as the instrument slightly shifts its adjustment from time to time, different parts of the spectrum may be used, the correct part being ascertained from time to time by trial. lVhile obviously my invention is not limited to the use of such types of prisms, and some may prefer achromatic prisms, the adjustments should, for the best results. be made on the yellow of the spectrum, if chromatic prisms are used.

Fondaylight work, as, for example, in the Forestry Service, the advantage of' the spectrum might be outweighed by the disadvantage or" not being able to see llolaris so distinctly with chromatic as with achromatic prisms. Obviously my invention is not restricted in its use to either ot' said types of prisms.

For daylight use, it might prove more practicable to have my invention so graduated that the approximate sideral time could be set by means of these gradnations and a fixed pointer or other mark on the transit rather than by means of lining up an element of my invention on two stars. The presence of such graduations might conversely be used to ascertain the approximate sideral time when the invention is lined up by means of two stars. My invention in its broadest aspect comprehends such mode of use.

Referring again to the specifically dis! closed mode ot use involving prisms, it is clearly to be understood that the retraction ot the line of sight may, within the scope of my invention, be obtained by any suitable means.

Referring more particularly to the drawing, I have at 1 in Fig. 1 indicated an ordinary surveyor-s transit having a telescope 2. Obviously any like or equivalent instrument may be employed. Assuming that the invention is used in connection With a surveyors transit. such instrument is set up at the station and the plates thereof are set at zero with the transit pointing along the orienting line whose directionis to be determined.- Having thuspositioned the tele` scope, the attachment constituting the simplest embodiment of my invention is now placed upon the outer end of the telescope.

This attachment comprises a tube 3 which may desirably be of brass 13 cm. long and 1 mm. thick and of such interior diameter as to give a slip t over the end of the teletsiaeei scope. For example, this may be 3.7 cm. for most telescopes in use in coast artillery schools. Graduations 40 may be provided on thetube 3 from which, through the fixed indicating line i1 on the telescope, the sideral time may be read. Desiralily and about 1Q()o apart I provide upon the rear end of the cylinder three slits 3 ot suitable length. At a suitable distance and desirahly about 2 cm. trom the end 4.- of the tube 3, l provide a 'flat ring 5, 6. lhis ring may be formed ot one integral piece or as distinct inner and outer members, or il: desired the inner member of the ring may be omitted. Desirably this ring is about 3 mm. wide and 3 mm. deep, and the inner portion (S thereof" constitutes a stop to prevent the attachment from sliding too tar onto the telescope Q. The outer portion of the ring constitutrs a support 'for the so-called straight-edge T, which, as most clearly shown in Fig. L). is preferably integral with the portion V ol' the ring. This straight edge is desirably about l5 cm. long and Q min. deep, and desir-ably one end is marked with the letter P indicating that such is the Polaris end or" the straight edge (thus indicating its preferred Inode ot use). I may also provide a small knob or pin S projecting slightly 'from the straight-edge to indicate in the darkness which is the P end.

lVithin the front end ot the cylinder of the attachment, I position preferably a pair of prisms 9, 10 carried by suitable rings o1' supports 11, 12 and in connection therewith I provide adjusting means here taking the form ot set screws 1?), the function of which will he hereinafter more fully set forth.

In the disclosed embodiment of my in vention, the pair of prisms are composed of ordinary spectacle glass and are so set that they will deflect the line ot sight from the axis of the cylinder by an angular amount ot lO T 5, that being taken as the average olf' the second and third extreme variations in the polar distance of Polaris following the assumed date of adjustment (August 1919). Desirably the prisms are not achromatic, and the result is that Polaris, as stated, instead of appearing as a point ot light, appears as a thin spectrum having a length of between 1 and 2 of are, and the adjustment is desirably made on the yellow of the spectrum.

In Fig. 3, I have indicated the axis ot collimation and have also indicated the lim` of sight which is deflected therefrom by said angular amount of 1o 7 5". The plane ol' sight i. e. the plane determined by the line ol sight and the retracted line of sight, intersects the P end or Polaris end of the straight-edge at an angle of 18 21.5', that being taken as a similar average with respect to the value of the angle A of the astronomical triangle indicated in Fig. 6.

The reason for these averages will be hereinafter set forth. l

The prisms are secured in place desirably as stated, by means of the inner' rings 11, 12, in which they are respectively secured by means of wax or other suitable adhesive used for this purpose. As such connecting means is old and Well known in the art, the same is not shown. The rings 11 and 12 are mounted with a close 'sliding fit in a sleeve 14, in the rear end of which sleeve is a ring 15 which may be locked in position by a set ,screw 16, While the front end of the sleeve is provided with a flangedl ring -or cap 17 which `may be locked in place on the sleeve by a set screw 18. y

To permit of proper adjustment of the prisms, the ring 15 is provided with a pair of spaced apart lugs 19-19 which are adapted to receive the adjusting screws 13-13, the adjacent ends of which abut against a lug 2O extending inwardly from the ring 12 so that, by backing out one screw 13 and threading in the other, the ring 12 with its prism 10 may be rotated through a deinite angle. The cap 17 is likewise provided with spaced apart lugs 21-21 adapted to receive the adjusting screws 13-13, the adjacent ends of which abut against a lug 22 extending over the ring 11 so that the ring 11 may be turned through an angle as just set forth in regard to ring 12.

Any other suitable means for securing and adjusting the prisms in place may be provided. One alternative method shown in Figs. 7 and 8 is to rotate one prism on the other until the desired degree of refraction is obtained, fastening them together by the use of balsam or other suitable substance.

When the prisms have been roperly adjusted and secured together they are fastened betfween vthe tapered rings 25e-'25, which rings are secured by suitable means such as the set screws 26-26 within a sleeve 27 and mounted in the forward end of the cylinder 28 of the attachment. The sleeve y 27 may be secured in position in the cylinder I28 by means of the clamping screw 29. A

casing in the form of a ring 30 may be provided to encircle the flange of the sleeve 27 and the forward end of the cylinder 28 and form a guard to preserve the clamping screw from accidental loosening thereof. ln this form of device a straight edge is formed on; the ring 31, which. encircles the cylinder 20 and forms an abutment for the rear end of the casing 30. Y

The telescope is now sighted and the tube 3 is rotated until the straight-edge 7 is lined up with Polaris and Ursae Minoris, the observer looking along the outside of the telescope. llt will be observed that the straightedge forms a certain denite angle with the plane of si ht, this being equivalent to setting the si eral time.

The intersection of the cross wires of the telescope are brought onto Polaris at the same time that the straight-edge is lined up as stated with Polaris and (5 Urs Minoris. The attachment may now be removed. The line of sight is now pointed due north; i. e., at the center of the circle described by Pon laris, i. e. the Celestial North Pole, and the azimuth of the reference line can be easily read and determined. It will be found that the angle on the vertical arc is the latitude.

The intersection of the cross hairs or cross lines should be brought on the yellow of the spectrum. As the time of year changes or as the instrument slightly shifts its adjustment from time to time, different parts of the spectrum may be used, the correct part being ascertained from time to time by trial. Desirably a color card is issued with each attachment showing the corlrect part of the spectrum to use each month.

.Un account of the nearness of Polaris to the pole, its right ascension and polar distance are chanO'ing rapidly and extensively.

I have, in describing my invention, .referred to the lining up of the straight-edge on Polaris and Urisae Minoris. Within the principle and scope of my invention the straight-edge may be lined up with Polaris and some otherstar, but for reasons herein indicated the best results are obtained by lining u the straight-edge on Polaris and Ursae `noris.

Polaris is the nearest bright star to the Celestial North Pole, Ursae Minoris is the brightest star near Polaris, is at a convenient distance for lining upon the straightedge with Polaris, and changes its position in the sky so slightly as not to necessitate freiuent readjustment of my invention.

li y invention may be employed for determining the true north in the Southern Hemisphere, by causing the transit to point 'to the Celestial South Pole by means of some two or three bright stars in the Celestial Southern Hemisphere.

lt will be observed that the straight-edge 7 corresponds. to the side A1B of the astronomic-al triangle, and that the an le Avis the same as the angle Y indicated in ig. 2, and is therefore the same value as the angle X indicated in Fig. 2 as 18 21.5

The disclosed embodiment of my invention constitutes a very simple means of north-determination. If adjusted biennially, its extreme error willy be well within the limits of precision necessary to heavy artillery orientation, and its average error in practice is negligible and easily reducible to zero. For :field artillery the attachment of my invention is sufficiently precise to become the sole method of astronomical north-determination.

In determining the true ncfrth, the prin- I stead of two stars increases the variability nection with some other star than Polaris, but itis desirable to use the same in connection with Polaris becauseof the relatively small polar distance thereof.

In fact the principle of my invention is applicable to any two stars within convenient distance of either the North or the South Celestial Pole, and the scope of my invention is such as to comprehend such use thereof.

In determining the true north, my invention may be employed with circumpolar stars, either north or south, and the straight edge is lined up with two such stars. The telescope or other sighting instrumentality is provided with means for deflecting the 'line of sight from the line of collimation of said telescope or other instrumentality by an angle equal to the mean polar distance of a circumpolar star. The use of three inof the accurac of the instrument. Therefore, preferab y I use .the same as hereinbefore described, but my invention is not limited to such described use.

Having thus described one embodiment of means pertaining to my invention and the best mode known-to me for practising the same, I desire it to be understood that although specific terms are employed, they are used in a generic and descriptive sense and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims:

1. Means for north determina-tion consisting of a mechanical substitute for computation involved in the so-called hour-angle method of north determination, comprising an attachment for `a telescope or similar sighting instrumentlity, an element carried by the attachment and adapted to be lined up on two stars when the cross hairs of the sighting instrumentality are brought on one of said stars and graduations associated with the said element whereby the y sideral time may be determined.

2. Means for north determination consisting of a mechanical substitute for the computations involved in the so-called hour angle method of north determination, comprising an attachmenta for a telescope or similar sighting instrumentality, an element carried by the attachment and adapted to be .lined up on two stars when the cross hairs of the sighting instrumentality are brought on one of said stars for the purpose of determining sideral time and means carried by the attachment for deliecting the line of sight of the sighting instrumentality from the line of collimation by an angular amount equal to the north or south polar distance of a given star.

'3. Means for determining the true north as well as latitude and sideral time, com- .sighting instrumentality .prising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined up with circumpolar stars when the crossl hairs of the sighting instrumentality are brought on one of said stars, associated means for defiecting the line of sight from the line of colli- `:nation of said telescope or instrumentality by au angle equal to the mean polar distance of the star upon which the cross hairs are brought, whereby the line of collimation is caused to point true north or south at an angular elevation equal to the latitude of the place of observation, and graduations and an indicator associated with the element whereby the partor element lined up with thetwo stars is caused to indicate the sideral time of the observation.

4. Means for determining true north as well as latitude and sideral time, comprising an attachment for a telescope or similar sighting instrumentality, a straight ed e carried by the attachment and adapted to he lined up with circumpolar stars when the cross hairs of the sighting instrumentality are brought on one of said stars and associated means for deflecting the line of sight from the line of collimation of the said telescope-by an angle equal to the mean polar distance of a certain polar star whereby the line of collimation is forced to point truenorth or south at an angular elevation equal to the latitude of the place of observation.

5. Means for determination of sideral time comprising an attachment for a telescope and a straight edge carried by the attachment and adapted to be lined up with two circumpolar stars when 'the cross hairs of the sighting instrumentality are brought on one of said stars, the position of said strai ht edge indicating the sideral time.

6. eans for north-determination comprising a telescope having a straight edge adapted to be lined u with two heaven y bodies when the cross airs of the telescope are brought upon one of said bodies and. prismatic means for deflecting the line of sight from the line of collimation of the with which said means for north-deternnnation is employed by an angle equal to the mean polar distance of one of said heavenly bodies.

7. Means for north-determination comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined up with two north or south circumpolar stars when the cross hairs of the sighting instrumentality are brought upon one of said stars, and associated means for deflecting the line of sight from the line of collimation of said telescope or instrumentality by an angleequal to the mean polar distance of a north or south circumpolar star.

8. Means for north determination com- A neiaeoi to the mean polar distance of one of said y stars.

9. Means for north-determination com- Y prisinel a telescope or other sighting instrumenta 1ty having a straight-edge adapted to be lined up with `Polaris and another body in the heavens when the cross hairs of the sighting instrumentality are brought upon Polaris and one or more prisms carried by said telescope or instrumentality and adapted to delect the line of sight from the line of collimation by an angle equal to the mean polar distance of Polaris.

10. Means for north-determination comprising a telescope havin Ia straight-edge tangent to a ring thereof a apted to be lined upj with Polaris yand another body of the heavens when the cross hairs of the telescope are brought upon Polaris and prismatic means for. delecting the line of sight from the line of collimation of the telescope by an angle equal to the mean polar distanceot Polaris.

11. A telescope attachment comprising a ring having a Astraight edge tangent thereto,

and prismatic means adapted to deflect the line or sight from the line of collimation of the telescope to which the attachment is applied lby an angle equal to the mean polar distance of Polaris. y

12. Means for north-determination comprisin in combination with sighting instrument ty an element or instrumentality adapted to be lined up with Polaris and B Ursee Minoris when the cross hairs of the sighting instrumentality are brought ',upon- Polaris and co-acting means to deflect the line of sight from the line of collimation of the sighting instrumentality to which said means for north-determination is applied, by an angle equal to the mean polar distance of Polaris, whereby the sighting instrumentality is pointed at'the Celestial North Pole.

13. Means for north-determination comprisingla straight-edge adapted to be lined up wit two of the heavenly bodies when the cross hairs of the sighting instrumentality with which said means of north determination is employed are brought upon one of said bodies, and means for deecting the line of si ht `from the line of collimation of the sighting instrumentality, by any angle equal to the mean polar. distance v`of one of said heavenly bodies.

14. rPhat method of north-determination comprising' sighting a telescope or like instrumentality, lining up an element of the telescope upon Polaris and another body in the heavens so as to obtain one side of the astronomical triangle and simultaneously delecting the line of sight of the telescope from the line of collimation by an angle 'equal to the mean polar distance of Polaris whereby the telescope is pointed at the Celestial North Pole.

15. Means :tor north-determination comprising a telescope having a straight edge exterior to the tube thereof adapted to be lined up on Polaris and another heavenly body when the cross hairs of the telescope are brought upon Polaris and prismatic means for defiecting the line of sight from the line of collimation of the telescope by an angle equal to the mean polar distance of Polaris.

16. That method of north-determination comprising sighting a telescope or like instrumentality, lining up an element of the telescope u on two heavenly bodies so as to obtain one side of the astronomical triangle and simultaneously deleoting the line of sight of the telescope from the line of collimation by an angle e ual to the mean polar distance of one o said heavenly bodies, whereby the telescope is pointed at the Celestial North Pole.

17. Means for determining the true north as well as latitude and sideral time, comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined up with circumpolar stars when the' cross hairs of the instrumentality are brought upon one of said stars, associated means for delecting the line of sight from the line of collimation of said telescope or instrumentality by an angle equal to the mean polar distance of one of said stars, whereby the line of collimation is caused to point true north or south at an angular elevation equal to the latitude of the place of observation, and graduations and an indicator associated with the part or element whereby the part or element lined up with the two stars is caused to indicate the sideral time of the observation, the mean polar distance being taken as an average between the maximum and the minimum polar distance oit the star used next succeeding the date of adjustment of the means for north determination.

18. Means for determining the true north as well as latitude and sideral time, comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined up with circumpolar stars when the cross hairs of the instrumentality are brought u on one of said stars, associated means for de ecting the line of sight from the line of collimation of said pole to the star whose polar distance is considered, next succeeding the date of adjustment of the means for north-determination.

19. Means for north-determination comprising a telescope or cylinder having a straight-edge or other part associated therewith and adapted to be linedup with two heavenly bodies when the cross hairs of the telescope orcylinder are brought upon one of said bodies and associated means for deflecting a line of sight from the line of collimation of the telescopeor cylinder with which said means for` north-determination is employed by an angle equal to the mean polar distance of one of said heavenly bodies, the' deflection being radial with respect to the ap arent orbit of said heavenly body.

20. cans for north-determination"comprising a telescope or cylinder having a 'straight-edge or other part associated therewith and adapted to be lined up with two north or south circumpolar stars when the cross hairs of the telescope or cylinder are brought upon one of said stars, and associated means for deHecting the line of sight from the line of collimation of the telescope or cylinder with which said means for northdetermination is employed by an angle equal to the mean polar distance of one of said( stars, the deflection being radial with respect to the apparent orbit of the star whose mean polar distance is selected.

21. Means for north-determination comprising a sighting instrumentality having a straight-edge or other part associated therewith and adapted to .be lined up withftwo heavenly bodies when the cross -hairs of the instrumentality are brought upon one of said bodies, and prismatic means for d eflectingnthe line of sight from the line of collimatiorf of the sighting instrumentality with which said means for north-determinationl is employed byan angle equal to the mean polar distance of one of said heavenly bodies, the deflection being radial with respect to the apparent orbit of said heavenly body.

22. Means for north-determination comprising a sighting instrumentality having a straight-edge or other part associated therewith and adapted to be lined up with two north or south circumpolar stars when the.

cross hairs of the instrumentality are brought upon one of said stars, and prismatic means for deflecting the line of sight from the line of collimation of the sighting instrumentality with which said means for north-determination is employed by an angle equal' to the mean polar distance of one of said stars, the deflection being radial with respect to the apparent orbit of the star whose mean polar distance is selected.

23. Means for north-determination comprising a telescope having a straight-edge tangent to a ring thereof and adapted to be lined up with Polaris and another heavenly body when the cross hairs of the telescope are brought upon Polaris and prismatic means for defiecting the line of sight from' the line of collimation of the telescope by an angle equal to the mean polar` distance of Polaris, the deflection being radial with respect to the apparent orbit of Polaris.

24. A telescope attachment comprising a ring having a straight-edge tangent thereto, and prismatic means adapted to deflect the line of sight from the line of collimation of the telescope to which the attachment is ap plied by an angle equal to the mean polar distance of Polaris, the deflection being radial with respect to the apparent orbit of Polaris.

25. Means for -north-determination comprising af telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined up with two heavenly bodies when the cross hairs of the telescope or instrumentality are brought upon one of said bodies, and associated means for deflecting the line of sight from the line ofcollimation of said telescope or like instrument by an angle equal to the mean polar distance'of a circumpolar star.

26. Means for north-determination comprising a telescope or other sighting instrumentality having a straight-edge adapted to be lined up with two north or south circumpolar stars when the cross hairs of the telescope or sighting instrumentality are brought upon one of said stars, and one or more prisms adapted to be carried by said telescope or instrumentality and adapted to deflect the line` of sight from the line of collimation by an angle equal to the mean polar distance of a circumpolar star.

27. Means for north-determination comprising a telescope or cylinder having a straight-edge tangent to a ring thereof and adapted to be lined up with heavenly bodies when 4the cross hairs of the telescope or cylinder are brought upon one of said bodies, and prismatic means for deflecting the line of sight from the line of collimation of the telescope by an angle equal to the mean polar distance of a heavenly body:

28. A telescope attachment comprising a ring having a straight-edge tangent thereto, and prismatic means adapted to deflect the line of sight from the line of collimation of the telescope to which the attachment is applied by an angle equal to'the mean polar distance o a heavenly body.

29. Means for north determination comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined-up with two north or south circumpolar stars, when the cross hairs of the sighting instrumentality are brought upon one of said stars and associated means for deflecting the linel of sight from the line of collimation of said telescope or instrumentality by an angle equal to the'main polar distance of one oit Said stars, the angle between the plane of sight and the lined-up part or element being taken as the average between the maximum and the minimum values (next succeeding the date of adjustment of the means for north determination) of the angle at the sighted star subtended by the Celestial North Pole and the other star.

30. Means or north determination comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined-up with two north or south circumpolar stars, when the cross hairs of the sighting instrumentality are brought upon one of said stars and associated means for deflecting the line of sight from the line of collimation of said telescope or instrumentality by an angle equal to main polar distance of one of said stars, the lining up not requiring any particular position of the eye of the observer.

31. Means or north determination comprising a telescope or sighting instrumentality, a part or element associated therewith and adapted to be lined-up with two north or south circumpolar stars, when the cross hairsA of the. sighting instrumentality are brought upon one of said stars and associated means for deflecting the line of sight from the line of collimation of said tele-scope or instrumentality by an angle equal to the main polar distance of one of said stars, the angle between the plane of sight and the lined-up part or element being taken as the mean value of the angle at the sighted star subtended by the Celestial North Pole and the other star.

32. Means for north determination comp/risinga telesco e or sighting instrumentality, a part or e ement associated therewith and adapted to be lined-up with two north or south vcircumpolar stars, when the cross hairs of the sighting instrumentality are brought upon one of said stars and associated means for deflecting the line of sight from the line of collimation of said telescope or instrumentality by an angle equal to the main polar distance of one of said stars, the angle between the plane of sight and the lined-up part or element being taken as the mean value of the angle at the sighted star subtended by the Celestial North Pole and the other star, said angle not being adjustable by the observer.

ln testimony whereof, I have signed my name to this specification.

ROGER SHERMAN HOAR. 

